The present invention relates to a multi-layer coil, and more particularly to a multi-layer coil using electro-condutive flexible sheets having electroconductive patterns.
Multi-layer coils have been used as voice coils for dynamic speakers and high frequency coils for radio communication apparatuses.
Coils using electroconductive flexible sheets are used with a view to simplifying the process to wind the conductor around a bobbin or a core. Furthermore, such coils are used with a view to preventing the precision of inductance from being deteriorated by unevenness of the winding pitch.
A coil using electroconductive flexible sheets, such as mentioned above, is described for instance in the Japanese utility model application laid-open Showa 59-192803, disclosed on Dec. 21, 1984.
In the utility model application,a conductor is formed over the flexible sheet, and this conductor corresponds to a coil of leading wire.
The conductor is formed over the flexible sheet so as to constitute a single continuous conductor when the flexible sheet is rounded into a cylindrical shape. The conductor over the flexible sheet is jointed. Therefore, when the flexible sheet is rounded, the conductor forms a single leading wire wound in the same direction to constitute a coil.
However, a coil described in the utility model application cannot be used as a voice coil for dynamic speakers or a high frequency coil for radio communication apparatuses. Thus, this coil involves the problem of not permitting a multi-layer structure because of its single-layer structure.
Furthermore, though it is conceivable to increase the number of single-layer windings to compose a high frequency coil, the space to accommodate the coils restricts the number of windings in such an attempt, resulting in the problem that no sufficient power to drive dynamic speakers could be derived.